2,630 research outputs found
Boundary conditions in the Dirac approach to graphene devices
We study a family of local boundary conditions for the Dirac problem
corresponding to the continuum limit of graphene, both for nanoribbons and
nanodots. We show that, among the members of such family, MIT bag boundary
conditions are the ones which are in closest agreement with available
experiments. For nanotubes of arbitrary chirality satisfying these last
boundary conditions, we evaluate the Casimir energy via zeta function
regularization, in such a way that the limit of nanoribbons is clearly
determined.Comment: 10 pages, no figure. Section on Casimir energy adde
Thermodynamics of conformal fields in topologically non-trivial space-time backgrounds
We analyze the finite temperature behaviour of massless conformally coupled
scalar fields in homogeneous lens spaces . High and low
temperature expansions are explicitly computed and the behavior of
thermodynamic quantities under thermal duality is scrutinized. The analysis of
the entropy of the different lens spaces in the high-temperature limit points
out the appearance of a topological nonextensive entropy, besides the standard
Stefan-Boltzmann extensive term. The remaining terms are exponentially
suppressed by the temperature. The topological entropy appears as a subleading
correction to the free energy that can be obtained from the determinant of the
lens space conformal Laplacian operator. In the low-temperature limit the
leading term in the free energy is the Casimir energy and there is no trace of
any power correction in any lens space. In fact, the remaining corrections are
always exponentially suppressed by the inverse of the temperature. The duality
between the results of both expansions is further analyzed in the paper.Comment: 21 pages, 2 figure
A calculation with a bi-orthogonal wavelet transformation
We explore the use of bi-orthogonal basis for continuous wavelet
transformations, thus relaxing the so-called admissibility condition on the
analyzing wavelet. As an application, we determine the eigenvalues and
corresponding radial eigenfunctions of the Hamiltonian of relativistic
Hydrogen-like atoms.Comment: 18 pages, see instead physics/970300
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